Defibrillators

AEDs (Automatic External
Defibrillators) are sophisticated, reliable, safe, computerised devices that
deliver electric shocks to victims of sudden cardiac arrest when the ECG rhythm
is one that is likely to respond to a shock. An AED can be used safely and
effectively without previous training. Therefore, the use of an AED should not
be restricted to trained rescuers.

Take look at this excellent video showing you what to do in an emergency: